The invention relates to an improved cutting head for mowing and trimming devices for grass, weeds and other vegetation, and more particularly to cutting heads equipped with flexible flails formed of cylindrical fibers.
The prior art is replete with mowing, trimming, and edging devices for the maintenance of lawns, the suppression of weeds and other applications of related nature. The bulk of this prior art technology relates to devices in which the cutting blade is a rigid member. Such mower, edgers, etc. have the great shortcomings that they cannot be operated near walls, trees or other solid obstructions for fear of damaging the cutting blade, and that if the blade should encounter a relatively small solid object, such as a stone or twig, the latter may be impelled into a trajectory where it can strike the device operator or a bystander and cause injuries.
One approach of the prior art, represented by U.S. Pat. No. 3,708,967 to Geist and Ballas and by U.S. Pat. No. 3,826,068 to Ballas, replaces the rigid cutting blade with one or more flails which are rotated in a plane by a central cutting head. At the high rotational speeds, the flexible flails are extended into substantially radial orientations by the action of centrifugal force and made sufficiently rigid to sever the relatively weak stalks of the vegetation to be cut. Because of their inherent flexibility and their low mass the flails overcome the aforementioned difficulties of the rigid cutting blades when encountering a solid object. Their tendency is to deform around the object, rather than break, or to launch the object into a random flight.
The referenced prior art Patents teach the use of a substantially cylindrical cutting head from which the flails extend radially, usually through vertical slits in the periphery of the cutting head. The trailing edges of such slits are curved, so as to prevent the imposition of high stresses at the root of the flail while deforming around an obstacle, thereby reducing breakage and wear.
While these measures of the prior art tend to reduce the incidence of breakage in the flexible flails which form the cutting blades of the improved cutting device, they do not eliminate the incidence of rupture and do not protect the flails when operated in close proximity to solid objects, such as walls, railings, trees, etc. In particular, they cannot protect the flails when deflected upwardly or downwardly out of the cutting plane, or when caught between the periphery of the cutting head and a rigid object.
It is, therefore, a primary object of the present invention to provide an improved cutting head for flail-type vegetation cutters with improved protection for the flails against abrasion and shear damage in operation.
It is an object of the invention to provide such an improved cutting head which is particularly adapted for use with flails of nylon monofilament.
It is also an object of the invention to teach the construction of improved cutting heads for rotary mowers and the like, which are simple to manufacture, easy to use, and reliable in service.